I had the same question and speculation a long time ago and somebody answered me... so I'll based on what he/she said.
Spoiler for What's behind the Amnesia Thing...:
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Originally Posted by Iareconfus
1.Was it Sakakibara that killed Reiko 1 year and a half ago?Him and the killer are very alike.
No. They're not the same person. It's purely coincidence.
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Originally Posted by Iareconfus
2.Does that have to do anything with the fact that he doesn't remember Izumi and their hand shook?If yes ,what do they have in common? If not,why can't he remember Izumi?
It's the curse itself that kept people from remmbering. It somehow affected Sakakibara since he's a relative of Reiko. Izumi has no knowledge about Reiko so she is spared... I guess